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Topic: Buffers and passive volume pedals: I'm confused. |
Jim Robbins
From:
Ontario, Canada
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Posted 4 Nov 2017 8:59 am |
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Question for those of you who understand this stuff. When I refer to volume pedals I'm referring to passive volume pedals.
First, here is my (perhaps mistaken) understanding of the facts:
1) High impedance volume pedals are better for psg than low. Less 'tone suck' i.e. roll off of highs. More gradual taper. I have 470K pots in my volume pedals.
2) Buffers reduce impedance a lot.
3) Lower impedance signals are good for a long signal chain i.e. multiple effects pedals & long cords - less loss of signal.
4) Lots of pedals including Boss TU2 tuner (which I have) have built in buffers.
5) Buffer or at least quality buffer should be the first thing after the pick up.
6) Low impedance signal into high impedance volume pedal messes up the taper so all the boost comes when you open the pot up wide (there seems to be a big difference in taper if I put the volume pedal right after the pick up rather than after the signal chain with its buffered pedals, but maybe it's just placebo effect).
Now the questions:
How to reconcile points 5 & 6 -- if you want your pickup to 'see' the buffer first, should you put your passive v.p. after it even though it will mess up the taper? Or does it matter to the buffer if the passive v.p. is between it and the pick up?
If the v.p. is after the buffer in the signal chain, would it be better to have a low impedance pot in it? If the signal to the v.p. is low impedance, would that avoid the 'tone suck' issues with low impedance v.p. and solve the taper issue?
I know one answer is "try it out, see what sounds best for you". However, I don't have any dedicated buffers or low impedance volume pedals kicking around (although I have been thinking about a Sarno black box). Ideally, I'd put my v.p. at the end of the signal chain.
Thanks in advance for your advice / observations. |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 4 Nov 2017 8:51 pm Re: Buffers and passive volume pedals: I'm confused.
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| Jim Robbins wrote: |
| If the v.p. is after the buffer in the signal chain, would it be better to have a low impedance pot in it? If the signal to the v.p. is low impedance, would that avoid the 'tone suck' issues with low impedance v.p. and solve the taper issue? |
Yes, and yes.
My preferred setup has a 1Mohm in / <5Kohm out buffer first, followed by a 50Kohm VP. That's about ideal for such a setup, with a constant - light - load on the PU, light enough load on the buffer, and reasonable low impedance feeding the cables to the amp.
Whatever taper the VP pot has, won't be altered by having a buffer before it.
However, comparing taper with and without a buffer, must take into account that a pot is not "directional" - load and signal can go both ways. Cable capacitance and amp-input impedance after the VP will be added to the load of the VP itself, i.e. the VP's input characteristics varies with the VP's position. The PU coil's own characteristics and output level will therefore vary with the varying load it sees through the VP, while no such variation will affect the PU when there's a buffer before the VP.
That explains most "with or without buffer" differences - including "tone suck" and "taper" variations - one can, and will, experience. |
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Robert Parent
From:
Gillette, WY
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Posted 5 Nov 2017 5:35 am
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1,2,3,5 = Yes.
4 Yes and No. While many pedals buffer the signal their input impedance is typically not really high enough for a PSG pickup. Input impedance needs to be at least 10x the output impedance of the input signal, more is even better.
A passive VP connected to the PSG pickup directly will change your tone as the volume is changed via the pedal.
What I have found after many years is the first item in the signal chain needs to be a very high input impedance buffer (1Meg or so). I built one using a LF353 opamp which works great. I follow the buffer with the passive VP and then into a combo amp or rack system.
Robert |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 5 Nov 2017 7:46 am Re: Buffers and passive volume pedals: I'm confused.
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| Jim Robbins wrote: |
...
6) Low impedance signal into high impedance volume pedal messes up the taper so all the boost comes when you open the pot up wide (there seems to be a big difference in taper if I put the volume pedal right after the pick up rather than after the signal chain with its buffered pedals, but maybe it's just placebo effect). ... |
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I disagree with this statement a bit. Low impedance into a high impedance volume pedal doesn't really mess up the taper. It actually is more likely to let the pot in the VP give it's true taper. When there is no buffer, then when at the top of the VP, the pot begins to expose the cable run to the pickup itself which presents more capacitance to the pickup and alters its tonality and response. With a buffer in place, the tone and taper are more correct and unaltered. So it could be argued that without a buffer, that's when you mess with the taper and sound.
Also, to comment on impedance; we're talking about 2 impedance issues when we talk about buffers. First is the "input impedance". That's the impedance that the pickup sees, and it very dramatically affects the tone of the pickup. Most pickups are designed around a 500kOhm load as found in the common volume pedal pots we use. Some active volume pedals and buffers will go higher than 500k, but many of us have found that above 500kOhms, the pickup tone becomes unpleasantly bright and harsh. With the devices out there that offer variable input impedance (FreeLoader, Black Box, Telonics vp, Revelation pre, etc.) it's been shown by many players that the real sweet spots for pickup tone tend to be in the 150kOhm to 350kOhm range for input impedance or "loading". That's where the strong treble peak of the pickup gets tamed and balanced out with the rest of the tone for a full, warm, clear, sweet response. When the input load impedance gets too high, we then spend our efforts at the amplifier or preamp trying to fix that harshness or excessive brightness.
The other impedance we're talking about here is the "output impedance" of the buffers. Buffers are made to have very low output impedance. This is where we gain the benefit of being able to drive long runs of cable without tone loss from cable capacitance. But the reality is that when we come out of a buffer and then thru a 500k volume pot pedal, the impedance of the cable run is made fairly high again because of that 500k pot. But in practice this really isn't a problem unless one uses very long cables (over 15'). In that case you may hear some darkening of the highs. But the advantage here is that the cable capacitance can never react to the pickup directly because there's a buffer between them. This means that the pickup's tone will remain consistent, no midrange shift, honkyness, or dulling of the pickup itself.
So in my experience, we often get the best tones with a buffer before the volume pedal with an input impedance in the 150kOhm to 350kOhm range. That does vary with different pickups, and there will be pickups and tone approaches that call for impedance loads higher and brighter than that range. But after 15 years of getting feedback from steel players regarding their impedance (vari-z) settings, this seems to be a popular range for those with the variable control over load impedance.
And regarding placing the volume pedal after your effects pedals. I would be careful there. Many pedals, Boss included, can not cleanly handle the high voltages that come from a steel guitar pickup. Some pickups can powerfully distort a Boss delay or reverb pedal. And by nature, a reverb or delay pedal should always be AFTER the volume pedal to properly do their thing. And by being after the volume pedal, the signal hitting these pedals will be greatly reduced and will prevent unwanted distortion.
Brad
www.sarnomusicsolutions.com |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 5 Nov 2017 8:53 am Re: Buffers and passive volume pedals: I'm confused.
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| Brad Sarno wrote: |
| So in my experience, we often get the best tones with a buffer before the volume pedal with an input impedance in the 150kOhm to 350kOhm range. |
That is about the load-range the PU sees in a passive setup with a 500Kohm VP followed by typical amp and cable load. So for those who don't want to alter eq settings on the amp when adding a buffer, a buffer in that load-range is pretty ideal. |
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Jim Robbins
From:
Ontario, Canada
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Posted 5 Nov 2017 9:10 am
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| Thanks very much for your responses which are giving me much food for thought. |
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Jim Robbins
From:
Ontario, Canada
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Posted 5 Nov 2017 9:13 am Re: Buffers and passive volume pedals: I'm confused.
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| Georg Sørtun wrote: |
| Brad Sarno wrote: |
| So in my experience, we often get the best tones with a buffer before the volume pedal with an input impedance in the 150kOhm to 350kOhm range. |
That is about the load-range the PU sees in a passive setup with a 500Kohm VP followed by typical amp and cable load. So for those who don't want to alter eq settings on the amp when adding a buffer, a buffer in that load-range is pretty ideal. |
So a buffer set like that before a long signal chain will give you something like guitar into passive vp into amp with relatively short cords? |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 5 Nov 2017 9:49 am Re: Buffers and passive volume pedals: I'm confused.
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| Jim Robbins wrote: |
| So a buffer set like that before a long signal chain will give you something like guitar into passive vp into amp with relatively short cords? |
"Something" like that, yes. The difference is that with a buffer in place, the load on the PU does not vary with VP travel. The PU load stays fixed as if the VP is left in one position. |
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Jim Robbins
From:
Ontario, Canada
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Posted 5 Nov 2017 12:17 pm Re: Buffers and passive volume pedals: I'm confused.
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| Georg Sørtun wrote: |
| Jim Robbins wrote: |
| So a buffer set like that before a long signal chain will give you something like guitar into passive vp into amp with relatively short cords? |
"Something" like that, yes. The difference is that with a buffer in place, the load on the PU does not vary with VP travel. The PU load stays fixed as if the VP is left in one position. |
Right, that makes sense insofar as I can grasp this stuff. Thanks. |
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Jon Jaffe
From:
Austin, Texas
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Posted 5 Nov 2017 12:31 pm
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| I know little about electronics, loads and such can be confusing. Craig Baker (RIP) explained the Little Izzy to me years ago this way. The Izzy was a small amplifier that did not add gain, or boost to the signal. But instead cleaned the signal up from the pickup so that it could travel smoothly down the imperfect pathway of the guitar cord. Actually, he recommended two Izzys one after the pot pedal to again clean up the signal again from the pedal to the stage amp. Volume pedals that use effects loops or have there own built in electronics like the Hilton, etc, may not need this. Please correct me if the oversimplification is wrong. |
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Jack Stoner
From:
Kansas City, MO
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Posted 5 Nov 2017 1:42 pm
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The Lil Izzy was merely an op-amp buffer device, that provides a constant (fixed) impedance load to the pickup and provides a low impedance output. Nothing more. There are many devices that will do this, such as the Goodrich Matchbox, Matchbro and the Hilton Volume Pedal. Devices that also do it, more eloquently, include Brad's "Steel Guitar Black Box" an "Audiophile" tube unit that includes a variable (adjustable)Impedance load for the pickup.
Peavey even did it with the Session 500 but most didn't want to be bothered with the extra guitar cord.
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GFI Ultra Keyless S-10 with pad (Black of course) TB202 amp, Hilton VP, Steelers Choice sidekick seat, SIT Strings
Cakewalk by Bandlab and Studio One V4.6 pro DAWs, MOTU Ultralite MK5 recording interface unit |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 5 Nov 2017 4:20 pm
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| Jon Jaffe wrote: |
| Actually, he recommended two Izzys one after the pot pedal to again clean up the signal again from the pedal to the stage amp. |
You are right in that when using a buffer before a regular VP with 500Kohm pot, it may, in some cases, also make sense to have a buffer right after the VP, if long cables are used from the VP over to the amp. Most use reasonable short cables of high quality there though, or effect units are placed there, so few will notice any effect of having a dedicated buffer after the VP.
"Clean up the signal" is the wrong term though, as what any such buffer do is to feed the cables after it with signal from a low impedance output. That low impedance in effect pretty much "short-circuits" the cable, so it becomes more immune from ambient electric noise.
So, the signal doesn't get cleaner per se, but it does get less disturbed by other electric signal/noise sources in the area, and less affected by cable capacitance.
(Sorry for the long explanation, but I spent almost two decades building and tuning in buffers and line-drivers for local radio stations. Having to drive signal through both screened and unscreened cables that were a few miles long, without getting audible quality-loss, was the norm for those jobs.
Buffering a steel PU is a lot simpler, but still critical for a good result  ) |
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